Web应用FileReader数据传递至Google Apps Script客户端为空问题求助

我开发的Web应用包含多个文件输入元素，支持用户上传任意数量、不同类型的文件。我尝试将所有数据先存储在与输入元素数量一致的数组中：数组的每个元素包含对应上传文件的文件名、blob、mimetype数据；若用户未上传文件，则通过data属性（header）保存该行的空上传引用。

数据在浏览器控制台中可见，但从Google Apps Script客户端访问时返回undefined/空值/Null。我对FileReader不太熟悉，服务器端需要将每个blob在Google Drive中创建文件，并最终将URL存储到表格中。相关代码如下：

function saveFormData(){

  var fileInputs = document.querySelectorAll('tr.result-row td > input.upload');
  var firstUploadIndex = fileInputs[0].parentElement.parentElement.getAttribute('data-index');

  //Loop through all upload rows
  var uploads = []; //will be array of arrays of multi-uploaded files; each item inside belongs to 1 column in db
  Array.from(fileInputs).forEach(input => {

    var files = input.files; //object file list

    if(files.length < 1){ //if there's no file in the upload input
      var header = input.getAttribute('data-uploadtype'); //save the header name as reference
      var fileData = [header, '', '', '']; 
      uploads.push(fileData);
    } else { //if there's a file/s in the upload input
      var innerUploads = []; //array of data for each file
      //Loop through all these files
      for(var i = 0; i < files.length; i++){
        
        var currentFile = files[i]; 

        if(!currentFile) return; //if no current file, just in case
        const fr = new FileReader();

        fr.onload = (e) => {
          var data = e.target.result.split(','); //split current file
          var fileData = { binary: data[1], mimeType: data[0].match(/:(\w.+);/)[1], filename: currentFile.name };
          innerUploads.push(fileData);
        }
        fr.readAsDataURL(currentFile);
      } //CLOSES FOR LOOP
      uploads.push(innerUploads);

    } //CLOSES IF
  
  }); //CLOSES FOR EACH LOOP

  google.script.run.saveToDrive(uploads);

} //CLOSES FUNCTION

上传界面如下：

内容的提问来源于stack exchange，提问作者Jed Santos